The security of information, such as that transmitted by radio frequency waves, is emerging as a privacy, economic, security, and anti-terrorism issue. In spite of security technologies such as data encryption, information may be surreptitiously obtained by sensing the emissions of keyboards, wireless mouse pointing devices, computer monitors, security systems and such. Unintended listeners may receive the emissions of telephone systems outside the user's premises. Employees may make calls with cell phones and inadvertently transmit background sounds or conversations. Some restaurants, theaters, churches and other public places want to prevent cell phones or pagers from being used. In some cases the information represented by the signals may not be important, but the signals themselves interfere with nearby sensitive equipment. Thus it is important in many circumstances to contain emissions within, and/or to prevent emissions from penetrating, a certain room or building.
Prior solutions have typically used electrically conducting materials, such as wire mesh or sheet metal, to enclose the volume of interest. The conducting materials are mechanically and electrically connected together and then grounded. Installation is done by building an enclosure a layer at a time. For example, one method in use today is to weld steel plates together on six sides of a room, with an opening for a door, typically steel. This method is labor intensive, requires a highly trained labor force, may require heavy duty material handling equipment, and the resulting structure slowly loses its RF shielding ability over time as small cracks develop in the welds due to building motion and/or settling.
In areas requiring high security it is also desirable to be able to detect attempts to penetrate the protected area to, for example, install a secret listening or viewing device.
Accordingly, what is needed is a new material and a new method of construction to reduce the transmission of RF signals into or out of an enclosure which allows easier construction, does not deteriorate over time, and is tamper resistant. The ability to simultaneously reduce acoustic energy (i.e. sound) transmission from or into the enclosure is also desirable.